In the related art, a cam-switching device is well known in which two kinds of cams having different cam profiles are provided in a cam shaft, and the cam shaft is slid in an axis direction by a hydraulic actuator to selectively switch between the cams such that valve characteristics of intake and exhaust valves are variable (for example, refer to patent literatures 1 and 2).
The intake and exhaust valves are typically urged in valve closing directions by valve springs, respectively, and are opened when a rocker arm that swings by the cams presses the intake and exhaust valves against a restoring force of the valve springs. That is, in a cylinder operation during which the intake and exhaust valves are opened and closed, a contact pressure is applied between the cams and the rocker arm. Therefore, switching between the cams is performed on a base circle of each of the cams where the intake and exhaust valves are not lifted.